It seems that people don't really care that much about doctrinal differences. The degree of ambivalence rivals a paper or plastic decision at the supermarket checkout. You're far more likely to get a reaction over confronting the doctrine. Let it go. And then it's not just letting it go, but give it a listen.
Covenant theology and dispensational or premillennialism are vastly different approaches to the Bible. You will come to massively contradictory interpretational conclusions based on which direction you take. Evangelicals and fundamentalists are today appreciating covenant theology more than ever. The covenant theologians talk unity, but they also want to persuade toward their system.
A Ligon Duncan of T4G might accomplish the push toward covenant theology by preaching the covenant of redemption at a dispensationalist, Baptist church. The gospel-centered cover will allow for him to get around to these churches, and when he preaches the covenant of redemption, it seems pretty innocent. He's preaching covenant, and covenants are in the Bible. And he's preaching redemption, and redemption's in the Bible. If he preaches the covenant of redemption, then he's preaching two good things at once, a covenant and redemption.
If you were to ask most evangelicals or fundamentalists whether they believe in the covenant of redemption, I think they would say that they do. Of course they believe in redemption and God has promised redemption, right? And so they're on their way toward covenant theology by believing in this foundational covenant theology doctrine. It sounds like Ligon Duncan is just talking about the gospel, and salvation, and Jesus. He's lifting up the Lord, and everyone should be blessed by that. What he's actually preaching is covenant theology and indoctrinating his listeners with hopes of their going his way.
The covenant of redemption isn't in the Bible. Protestants kept amillennialism and needed a defense of it to make it compatible with sole scriptura, so they invented a system of interpretation of scripture that could defend it. It didn't come from reading the Bible. People who preach it are making up something in order to uphold a nonexistent infrastructure of the Bible. It is ironically non scriptura.
The Bible has pieces of what is found in the invented covenant of redemption, but not enough of it to merit its existence. The covenant of redemption stands within a narrative that was concocted to preserve amillennialism. To sustain a covenant of redemption, gaps must be bridged for the story to hold together. The true story doesn't have those gaps. Nothing needs to be contrived. It stands on its own. And the truth works that way because it comes from God, and God is comprehensive and congruous.
The most basic contradiction of the covenant of redemption by what God's Word teaches is that it isn't a covenant. We have actual covenants in the Bible -- Abrahamic, Mosaic, Davidic, and New. The Bible records no pre-creation conference or transaction between eternal Father and eternal Son in which the Father and the Son negotiated with one another about who would accomplish what in redemption, both parties receiving something from the other as a part of a grand bargain.
Amillennialism requires allegorization of eschatological passages, which are many, because the Bible is at least 25 percent prophetic. To exist, amillennialism needs minimization of distinctions within God's work in His history of redemption. In modern political and diplomatic language, this is called walking the story backwards. You start with your result and then you walk back the story to fit your preconceived notion. In one way, I hate to use this analogy, but I think it's true -- it's like what criminals do when they're caught and they need to tell a story that will leave everyone innocent. Some of it must be true, because the story won't work if the parts everyone already knows, that they can see or read, aren't what actually happened. The key to making up the story is to bring everyone together within the gaps in knowledge. That's what covenant theology did. The narrative process doesn't begin with the covenant of redemption, but it sounds like that's where the story starts, even though you don't read it in the Bible.
Of course, criminals are criminals. They robbed a house. They stole from a bank. They assassinated someone. In other words, they did something really bad. They didn't pervert a quarter of the Bible. They did something really bad. So Phil Johnson, Carl Trueman, and James White can sit together and laugh about their differences. They don't matter enough to separate. We shouldn't hang out with criminals, but it's OK to fellowship within the framework of a whole other narrative, a story of unity between people who disagree on hundreds of pages of scripture. There's a god somewhere that has no problem with that.
Plenty has been written exposing the unscriptural and non-scriptural nature of covenant theology and amillennialism. I'm not attempting to do anything close to comprehensive here as an expose. My problem is that wrong thinking about God, about history, about the future, about the present, about the will of God, and about how God works is allowed under the cover of a so-called "conservative" approach to the Bible. It isn't conservative. It doesn't honor God. It's a travesty.